1. FIELD OF THE INVENTION
This invention relates to a method of rolling a length of metal bar or wire, especially hot-rolled bar or wire, and is particularly concerned with the steps necessary to keep such a metal length stretched at the end of rolling when it passes through a cooling device after the final roll stand. The invention also relates to apparatus for carrying out the method. For ease of description, the metal length will generally be called a bar in the following description, but is not limited thereto.
2. DESCRIPTION OF THE PRIOR ART
It is known to keep a "continuous" metal bar or wire, which is passing through a finishing roll stand and subsequently through a cooling device, stretched by means of a set of bridle rolls (also known as pinch rolls) located after the cooling device, between which the bar is frictionally gripped. Typically the bridle rolls are driven by independent identical motors with a rated peripheral velocity exceeding the finishing rolling speed of the bar. See Dutch Pat. No. 154129, which discloses use of an adjustable parallelogram-shaped yoke in a plane at right angles to the passage of the bar, the yoke being supported by two fixed pivots above and below the rolls. The rolls turn in bearings in the upstanding sides of the parallelogram-shaped yoke. The motors are fitted in the said upstanding sides.
In practice, it has been found that, possibly owing to the large inertial mass involved, the first part of the bar becomes twisted or buckled in the cooling device. This is apparently caused by some difficulty of entry of the leading end of the bar into the bridle rolls, or some slippage in the grip of the bridle rolls, and occurs notwithstanding the slightly higher speed of the bridle rolls at entry of the bar. This higher speed arises from the power input to the motors of the rolls which is selected so that the rolls exert a drawing on the bar to keep it under tension. Bar ends damaged in this way have to be scrapped, which is costly.